11 year-old Nada al-Ahdal from Yemen tells her story of escaping from a forced marriage, and wants to stop the same thing happening to other children. Courtesy Memri TV

In May 2010, a 14-year-old girl in Victoria was banned from leaving Australia and her parents forced to surrender her passport to save her from an arranged marriage.

The girl had old her teacher that she wouldn't be attending classes anymore because she was due to travel overseas to be married. She was just 13. According to court documents, the girl's teacher contacted Victoria's Department of Human Services, which sent two officers to the girl's home while her parents were at work. The girl let them in, telling the workers that "she was not attending school because her father had said that he did not like her going to school" and because she was "engaged to be married and was planning to travel overseas in two or three weeks' time in order to meet her fiance ... she had only seen a photograph of this man".

When asked how she felt about getting married, the child said she "did not know what to say as she had not met her fiance". When asked if she understood whether she was expected to have sex, she indicated that she did not know what that really meant.

Two months later, a 17-year-old Sydney girl called Australian Federal Police and told therm she was being taken against her will by her mother to Lebanon to be married.

The girl told police that she might have to "hang up at any time" because she didn't have much freedom to use the phone. She wanted to be placed on the Airport Watch List so she could not be taken out of the country against her will.

In a third case, a Sydney girl aged 16 confided to a teacher that her parents were planning to take her abroad to marry a man she did not know.

Federal Magistrate Joe Harman noted that the application to have the girl's name put on the Airport Watch List was "becoming increasingly common before the court."

"The wedding has been planned to take place in a little under two weeks' time and would involve the child flying from Australia [to Lebanon] for the purpose of marriage".

He was able to put a stop to it, only because the girl had "betrayed, or at least bucked the authority of her parents" in approaching her teacher, but she was fearful for her personal safety once her mother became aware of the proceedings. Adding to the sense of urgency, there was some risk that if the girl's parents got wind of what was going on, she might be "spirited out of the country over the weekend" and nothing could be done to preserve her rights.

Figures released in 2011 showed that more than 200 17-year-old girls were granted prospective spouse visas over the past five years - a figure child safety campaigners branded as shocking.

Child brides are common in Yemen. Tehani, now 8, is seen with her husband Majed, 27, and her former classmate Ghada, 8, and her husband outside their home in Hajjah, Yemen. Picture: Stephanie Sinclair/UN - www.tooyoungtowed.org

Hundreds more 18-, 19-, and 20-year-old women also received the visas after being sponsored by older men. The majority of the teenagers were from the Middle East or Southeast Asian countries.

One 17 year old from Thailand was brought out by a 57-year-old man, and a 17-year-old Iraqi girl was sponsored by a 50 -year-old.

More than a hundred 17 year olds from Lebanon were granted the visas after being sponsored by men aged 19 to 37.

Incredibly, until this year, forcing underage girls into marriages - either here or overseas - wasn't a criminal act.

Former Attorney-General Nicola Roxon introduced the so-called Slavery Act as a direct response to increased reports of forced marriages and other forms of human trafficking.

Under the act, someone who forces a child into a marriage, which could include a child's parents, can be jailed for up to seven years.

The global scale of child marriage is staggering.

According to the United Nations Population Fund, 13.5 million girls around the world marry before their 18th birthday each year.

One in three girls in developing countries will probably be married before they are 18. One out of nine girls will be married before their 15th birthday.

Some are as young as five.

Sexual assault and death

They routinely face psychological and physical injuries, sexual assault and domestic violence, false imprisonment and estrangement from their family.

Figures from the UN Population Fund's Marriaed Too Young report show the prevalance of child marriages worldwide.

Girls under 15 are five times more likely to die in childbirth than women in their 20s, and girls age 15-18 are twice as likely to die, a study by the UN Population Fund found.

The children of girl brides are 60 per cent more likely to die by their first birthday than children with mothers over age 19.

The UN has launched a campaign to end child marriage by 2030, in a bid to free girls from poverty, ignorance and oppression at the hands of their husbands.

At the program launch, Un "elder statesman" Archbishop Desmond Tutu said he was as committed to abolishing child marriage around the globe as he was to fighting apartheid in South Africa.

The UN Population Fund says the number of underage girls being married off is rising rapidly and will hit 14.2 million a year by 2020, and 15.1 million a year by 2030, if the trend is not curbed.

The agency said the problem is mainly concentrated in South Asia and sub-Saharan Africa, where girls as young as five or six are married off.

The worst country for child marriage was Niger, where 75 per cent of married women age 20-24 were wedded before they were 18.

The UN Population Fund's executive director, Dr. Babatunde Osotimehin, called for all nations to set a mandatory marriage age of 18. In Australia, a bride or groom must be at least 18, unless a court has approved a marriage where one party is aged between 16 and 18.

Meanwhile, around the world, 37,000 young girls under 18 are married off - usually to older men - every day.

The world's youngest divorcee

Some, like Nujood Ali, manage to escape.

In 2008, Nujood was married off by her father at nine, for a dowry of a little more than $750, after her future husband, Faez Ali Thamer, promised not to have sex with her "before the year after she has her first period" - as required by law in Yemen.

But what followed was a cycle of sexual and physical abuse, starting on her wedding night.

Former child-bride Nujud Mohammed Ali was granted a divorce in 2008 at the age of eight after her unemployed father forced her into an arranged marriage with a man twenty years her senior. AFP /Mohamed Huwais

Two months later, during a visit back to her family home, she took the unprecedented step of running away and asking a court for a divorce on grounds of abuse.

Her story was turned into a best-selling book, I Am Nujood, Age 10 and Divorced, and gave hope to thousands of underage brides.

Now 15, it hasn't all gone to plan for Nujood. The royalties from her book were supposed to pay for her schooling and allow her to follow her ambition to become a lawyer.

Instead the money has been squandered by her father - who has now sold her younger sister to a man twice her age.

"My father has spent all the money on getting married twice again," she told The Guardian in March this year.

A NOTE ABOUT RELEVANT ADVERTISING: We collect information about the content (including ads) you use across this site and use it to make both advertising and content more relevant to you on our network and other sites.